Heavy metal concentration and bacterial contamination associated with selected leafy vegetables in Abeokuta Metropolis, southwest Nigeria

Abstract

The assessment of heavy metal concentration (Cu, Fe, Zn, Pb, Cd, Co and Cr) and bacteriological contamination in five (5) most consumed vegetables Talinum triangulare, Celosia argentea, Vernonia amygdalina, Corchorus olitorus and Telfaria occidentalis in Abeokuta Metropolis was carried out because the consumption of vegetables on display in markets and roadsides had been associated with gastro-intestinal disorders. The vegetables were randomly purchased from six markets within the metropolis and analyzed using standard procedures involving Atomic Absorption Spectrometry (AAS) and Standard Plate Count (SPC). The levels of heavy metals in leafy vegetables varied significantly (P < 0.05) across locations and were within World Health Organisation (WHO)/Food and Agricultural Organisation (FAO), permissible limits except for Pb and Co found in T. occidentalis, C. argentea, T. triangulare and V. amygdalina. Eleven species of bacteria including Bacillus subtilis, Escherichia coli, Microccoccus species, Staphyloccocus aureus, Klebsiella aerogenes, Staphylococcus saprophyticus, Proteus mirabilis and Bacillus megaterium were isolated from the leafy vegetables. B. subtilis was the most abundant (93.3% occurrence) while B. megaterium and S. aureus were least abundant (8% occurrence). Total colony counts of bacteria ranged from 1.51 x 10⁷ – 58.50 x 10⁷ (CFU/g) with V. amygdlina and Celosia argentea both from Elega having the lowest and highest values respectively.

The levels of heavy metals and bacterial contamination in selected vegetables were found to be unsafe. Public sensitisations on hygienic handling of vegetables from production to consumption in addition to frequent safety assessment are recommended to minimize human exposure to heavy metals and bacterial pathogens.